This application claims the benefit of the Korean Application Nos. P2001-40455 filed on Jul. 6, 2001, and P2002-23050 filed on Apr. 26, 2002, which are hereby incorporated by reference,
1. Field of the Invention
The present invention relates to circuit for driving a display of current driven type, and snore particularly, to circuit and method for driving a display of current driven type, in which a pre-charging static power source is provided separately for implementing a low power consumption.
2. Background of the Related Art
Recently, passing ahead CRTs (Cathode Ray Tubes) that have been used the most widely, the flat displays, shown up starting particularly from the LCD (Liquid Crystal Display) at the fore front, are developed rapidly in the fields of PDP (Plasma Display Panel), VFD (Vacuum Fluorescent Display), FED (Field Emission Display), LED (Light Emitting Diode), EL (Electroluminescence), and the like.
Because the foregoing displays of a current driven type have, not only good vision and color feeling, but also a simple fabrication process, the displays are widening fields of their applications.
Recently, an organic EL display panel is paid attention as a flat display panel that occupies a small space following fabrication of large sized display.
The organic EL display is provided with datalines and scanlines crossed in a form of a matrix, in which a light emitting layer is formed in each of crossed pixels. That is, the organic EL display panel is a display a light emitting state is dependent on voltages provided to the datalines and the scanlines.
For tight emission from each of the pixels, one of the scanlines is made by a scan driving part to select a power source in an order starting from the first scanline to the last scanline during one frame period, and the datalines are selectively made by a data driving part to receive a power for the same frame period, for emitting a light from a pixel at which the scanline and the dataline are crossed.
Though current-light emission characteristics of the organic EL display panel is almost not dependent on a temperature, the current-light emission characteristics shifts toward a high voltage side as the temperature drops. Therefore, because it is difficult to obtain a stable operation, if the organic EL display is operated on a voltage, a static current driving type is employed in driving the organic EL display,
FIG. 1 illustrates a related art circuit for driving an organic EL display panel.
Referring to FIG. 1, there is an anode of the organic EL pixel 103 having an Idd, a static current, supplied thereto through a static current source 101 and a switch for pixel 102. The static current source 101 controls the current to the anode of the organic EL pixel 103. A time the current is provided to the anode of the organic EL pixel from the static current source 101 is controlled by the pixel switch 102. That is, during the pixel switch 102 is turned on, the current flows from the static current source 101 to the anode of the organic EL pixel 103, and makes the organic EL pixel 103 to emit a light. In this instance, the turn on/off of the pixel switch 102 is controlled by means of a PWM (Pulse Width Modulation) waveform from the data driving part (not shown).
The PWM waveform for controlling turn on/off of the pixel switch 102 will be called as a data enable signal for convenience of explanation. A gray level of the organic EL pixel 103 is varied with a poise width of the data enable signal.
There is a scan driving part 104 of an NMOS driven by a scan signal, having a drain connected to a cathode of the organic EL pixel 103, and a source connected to another source voltage Vss,
The organic EL pixel 103 emits no light instantly even if a current is provided thereto through the pixel switch 102. That is, the organic EL pixel 103 emits a light taking a responsive time period, because a voltage charging time period to a capacitor (not shown) inside of the organic EL pixel 103 is required.
Due to above reason, light emission of the organic EL pixel 103 at a desired gray level is difficult, has a poor luminance too, and requires much current owing to the voltage charge to the capacitor.
Thus, the display of current driven type consumes the more current at the display and the driving circuit, as a size of the display panel becomes the larger. Moreover, since the higher the resolution, the more the current requirement for obtaining a desired luminance, the more current is required for obtaining a desired luminance.
This large amount of current requirement serves as an unfavorable condition for portable devices, and brings about an unfavorable result to a lifetime of a display.
Accordingly, the present invention is directed to circuit and method for driving a display of current driven type that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide circuit and method for driving a display of current driven type, in which a pre-charge system is employed for controlling a current amount.
Another object of the present invention is to provide circuit for driving a display of current driven type, in which a pre-charge timing is controlled for controlling a power for an entire system.
Further object of the present invention is to provide circuit and method for driving a display of current driven type, in which level and time of a pre-charge current are controlled for operation of a pre-charge within a range of a limited battery power so as to be suitable for application to portable devices.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the circuit for driving a display of current driven type includes an organic EL pixel, a scan driving part for making the pixel to emit a light in response to a scan signal, a first static current source for being controlled so as to be turned on/off in response to a data enable signal, to supply a current to the pixel, a second static current source for being controlled so as to be turned on/off in response to a precharge signal, to supply a current to the pixel for precharging the pixel, and a controlling part for controlling amounts of the currents from the static current sources.
The controlling part preferably controls a bias of the second static current source for controlling the amount of current from the second static current source.
In a case the organic EL pixel is burned on in rising synchronous, the second static current source is preferably turned on at a starting point of the scan signal, for starting precharge of the organic EL pixel.
In a case the organic EL pixel is turned on in falling synchronous, the second static current source is preferably turned on before the data enable signal is enabled, for starting precharge of the organic EL pixel.
Preferably, the precharge signal is a pulse width modulation signal, and a gray level of tile pixel is fixed according to a width of the precharge signal.
Preferably, the precharge signal is a pulse width modulation signal, and a precharge time of the pixel is fixed according to a width of the precharge signal.
Preferably, a plurality of static current sources designed in the driving circuit is turned on for use as the second static current source.
Preferably, the driving circuit further includes a first switch part for controlling turn on/off of the first static current source, the first switch part including a plurality of switch devices having drain terminals connected to the first static current source in common for being driven on reception of first to xe2x80x98Nxe2x80x99 data enable signals respectively.
Preferably, the driving circuit further includes a second switch part to be driven upon reception of the precharge signal for controlling turn on/off of the second static current source.
The control part is provided between one ends of the first, and second switch parts and a ground voltage terminal for being driven *upon reception of bias signals in common.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.